Photochemistry of benzophenone adsorbed on MCM-41 surface

The photochemistry of benzophenone adsorbed on a channel-type solid support MCM-41 was studied by the use of diffuse reflectance and chromatographic techniques. For comparison purposes parallel studies were also conducted on silicalite and H-ZSM-5. The observed ground state absorption, luminescence and transient absorption spectra and photoproduct distribution strongly depend on the substrate under study. Triplet state luminescence was observed in all solids, hydrogen-bonded excited benzophenone emission was detected on MCM-41 while protonated excited benzophenone luminescence was observed only on H-ZSM-5. Transient absorption showed the triplet state in all solids and formation of the OH benzophenone adduct on MCM-41 and H-ZSM-5. Ketyl radical formation occurs after 355 nm irradiation but is a minor degradation pathway. The formation of transients resulting from the reaction of benzophenone with molecular oxygen was also detected on MCM-41, in air-equilibrated conditions and benzoic acid is the main degradation product. 2-Hydroxybenzophenone is one of the major photodegradation products on MCM-41 and H-ZSM-5. Products resulting from the α-cleavage were also detected under 266 nm irradiation. Benzophenone was found to be very stable in silicalite under all used conditions.